1. Field of the Invention
The present invention relates to a process for exchanging halogen other than fluorine, preferably chlorine, for fluorine in organic compounds by means of hydrogen fluorine. The invention furthermore relates to bismuth/alkaline earth metal catalysts which contain 0.005-0.8 g-atom of bismuth per mol of the alkaline earth metal compound employed and can furthermore contain promoters and/or inert additives, and lanthanide catalysts with or without catalysts supports.
2. Description of the Related Art
A number of catalysts have been proposed for the exchange of halogen other than fluorine (mainly chlorine) for fluorine in halogenated organic compounds by means of hydrogen fluoride, the reaction chiefly being carried out in the gas phase, such as catalysts containing chromium and magnesium (European Patent 130,532), catalysts containing magnesium and iron and in addition copper and/or manganese (European Paten 235,547) and chromium oxide gels (U.S. Pat. No. 3,149,170); catalysts which consist of aluminum oxide containing halides of chromium, cobalt, nickel, copper, palladium or bismuth are furthermore known for the hydrofluorination of alkenes or fluoroalkenes to the associated fluorinated alkanes (DE-AS (German Published Specification) 1,900,241). Of the catalysts mentioned, the chromium oxide gels in particular have a high activity. However, their preparation and their use has the following disadvantages: When these gels are prepared from aqueous solution, considerable filtration difficulties must be reckoned with; however, the environmental measures which must be taken for disposing of chromium-containing residues form the preparation of these catalysts or of the spent chromium-containing catalysts themselves are of a particular and adverse significance.
There was therefore a need for processes for halogen-fluorine exchange in organic compounds using hydrogen fluoride, in particular in the gas phase, which can be carried out with a high fluorination activity and fluorination selectivity and which use catalysts which are free from chromium. The process according to the invention and the catalysts according to the invention meet this need.